A proposal has been made for a camera system in which, on having a plug-in unit having an image pickup device and an image-taking optical system integrated therein mounted on a camera main body, information on the plug-in unit is transmitted to a camera main body side so that photos can be taken with the image-taking optical system provided to the plug-in unit (refer to Japanese Patent Laid-Open No. 8-17256). If the camera system in which the image-taking optical system, that is, an image-taking lens is replaced just by mounting the plug-in unit on the camera main body is realized, handling of the camera system becomes so easy that a person without expert knowledge can easily replace the image-taking lens.
There is a similar camera system including a camera head having an image-taking optical system and an image pickup device and a camera main body having the camera head detachably mounted thereon that receives an image signal from the camera head and performs signal processing (Japanese Patent Laid-Open No. 2000-175089 for instance).
However, the specification of neither Japanese Patent Laid-Open No. 8-17256 nor Japanese Patent Laid-Open No. 2000-175089 has a description of a process in the case where a signal conversion processing section of the camera main body cannot perform signal processing to the image signal received from the camera head on the camera main body side with its capabilities.
In the case where these types of camera systems become widespread, the camera head and the camera main body may be sold separately so that they are bought after checking that they are compatible models. However, there are the cases where a user notices that they are incompatible for the first time on image-taking, that is, on mounting the camera head on the camera main body. Recently, there are also the camera heads including the image pickup device including a special CFA (Color Filter Array) having a four-color arrangement of emerald green in addition to R, G and B. It is predictable enough that, if such a camera head is mounted on the camera main body, there will be a situation where the signal processing cannot be performed with capabilities of the signal conversion processing section of the camera main body. It is extremely inconvenient if image-taking cannot be performed in such a case. Even if the image-taking itself is possible, a signal conversion process cannot be performed in the camera main body. Therefore, conversion to the image signal for display cannot be performed so that a subject normally displayed on a display screen is no longer displayed. If a direct-view finder is placed on the camera main body side of such a camera system, it may be possible to perform the image-taking by looking into the finder. It is inconvenient on performing the image-taking, however, if the subject is not displayed on the display screen.
In view of the circumstances, an object of the present invention is to provide the camera system and camera main body capable of performing the image-taking even with the camera main body including the signal conversion processing section having no capabilities for performing the signal processing to the image signal transmitted from the mounted camera head.
Another object of the present invention is to provide the camera system and camera main body capable of, even when having the camera head incapable of performing the signal conversion process mounted on the camera main body, having the subject displayed on the display screen and using the display screen instead of the finder on performing the image-taking.